Image projection apparatus

Abstract

An oblique projection optical system for leading rays of light from a display surface on which an image is displayed to a projection surface in such a way that the ray of light from the center of the display surface is obliquely incident on the projection surface in order to project a magnified image of the image displayed on the display surface onto the projection surface includes a plurality of reflecting surfaces having a power. At least two of the reflecting surfaces have a free-form curved surface, and, of all the reflecting surfaces, the one closest to the projection surface has a negative power and at least one of the other has a positive power. Alternatively, in a rear projection optical system having a projection optical system for projecting an image displayed on a panel display surface onto a screen surface, the projection optical system includes at least four curved-surface reflecting mirrors.

1. An image projection apparatus comprising a projection optical system for projecting an image displayed on a display surface onto a screen, the projection optical system including at least four curved reflecting surfaces,
 wherein the projection optical system does not form an intermediate real image of the display surface between the display surface and the screen, and 
 wherein, assuming that a ray of light that travels from a center of the display surface through a center of an aperture stop to a center of the screen surface is called a screen center ray, the following conditions are fulfilled:
   0.5< DL/HL< 3.5, 
   10<θ<70, 
   Fnoy≦3.5, and 
   Fnoz≦3.4, 
 
 where 
 DL represents an optical distance traveled by the screen center ray from a last surface of the projection optical system to the screen surface, 
 HL represents a dimension of the screen surface in a direction parallel to a plane formed at the center of the screen surface by a normal to the screen surface and the screen center ray, 
 θ represents an angle of incidence at which the screen center ray is incident on the screen surface, 
 Fnoy represents an f-number in a direction corresponding to the height direction of the display surface, and 
 Fnoz represents an f-number in a direction corresponding to the width direction of the display surface. 
 
   
   
     2. An image projection apparatus as claimed in  claim 1 , wherein the following condition is fulfilled:
   Fnoy≧Fnoz. 
 
   
   
     3. An image projection apparatus as claimed in  claim 1 , wherein the following condition is fulfilled:
   0.81< DL/HL< 3.5. 
 
   
   
     4. An image projection apparatus as claimed in  claim 1 , wherein the following condition is fulfilled:
   0.858< DL/HL< 3.5. 
 
   
   
     5. An image projection apparatus as claimed in  claim 1 , wherein the following condition is fulfilled:
   0.879< DL/HL< 3.5. 
 
   
   
     6. An image projection apparatus as claimed in  claim 1 , wherein the following condition is fulfilled:
   0.925< DL/HL< 3.5. 
 
   
   
     7. An image projection apparatus as claimed in  claim 1 , wherein the following condition is fulfilled:
   0.941< DL/HL< 3.5. 
 
   
   
     8. An image projection apparatus as claimed in  claim 1 , wherein the following condition is fulfilled:
   Fnoy≧3.4, and 
   Fnoz≧3.3. 
 
   
   
     9. An image projection apparatus as claimed in  claim 1 , wherein the following condition is fulfilled:
   Fnoy≧3.1, and 
   Fnoz≧3.1. 
 
   
   
     10. An image projection apparatus as claimed in  claim 6 , wherein the following condition is fulfilled:
   Fnoy≧3.4, and 
   Fnoz≧3.3. 
 
   
   
     11. An image projection apparatus as claimed in  claim 6 , wherein the following condition is fulfilled:
   Fnoy≧3.1, and 
   Fnoz≧3.1. 
 
   
   
     12. An image projection apparatus as claimed in  claim 1 , further comprising the screen, the screen including an optical member, the optical member having a Fresnel portion,
 wherein the Fresnel portion fulfills the following condition:
   [a pitch of the Fresnel portion]/[a size of a pixel of a projected image on the screen]<0.5. 
 
 
   
   
     13. An image projection apparatus as claimed in  claim 12 , wherein the optical member is a Fresnel lens. 
   
   
     14. An image projection apparatus as claimed in  claim 13 , wherein the Fresnel lens has a flat surface on a side thereof on which projection light is incident. 
   
   
     15. An image projection apparatus as claimed in  claim 12 , wherein the optical member is a total reflection prism array. 
   
   
     16. An image projection apparatus as claimed in  claim 9 , further comprising the screen, the screen including an optical member, the optical member having a Fresnel portion,
 wherein the Fresnel portion fulfills the following condition:
   [a pitch of the Fresnel portion]/[a size of a pixel of a projected image on the screen]<0.5. 
 
 
   
   
     17. An image projection apparatus as claimed in  claim 11 , further comprising the screen, the screen including an optical member, the optical member having a Fresnel portion,
 wherein the Fresnel portion fulfills the following condition:
   [a pitch of the Fresnel portion]/[a size of a pixel of a projected image on the screen]<0.5. 
 
 
   
   
     18. An image projection apparatus as claimed in  claim 1 , wherein a second curved reflecting surface as counted from a display surface side is disposed on a side of the display surface opposite to a first curved reflecting surface as counted from the display surface. 
   
   
     19. An image projection apparatus as claimed in  claim 18 , wherein the projection optical system has no optical axis that holds throughout the optical system. 
   
   
     20. An image projection apparatus as claimed in  claim 1 , wherein a portion of the projection optical system protrudes from the screen. 
   
   
     21. An image projection apparatus as claimed in  claim 11 , wherein the projection optical system has a free-form curved reflecting surface. 
   
   
     22. An image projection apparatus as claimed in  claim 1 , wherein the image projection apparatus is a front projection apparatus. 
   
   
     23. An image projection apparatus as claimed in  claim 1 , wherein the image projection apparatus is a rear projection apparatus. 
   
   
     24. An image projection apparatus as claimed in  claim 1 , wherein the projection optical system has a pupil plane positioned between the display surface and the curved reflecting surface closest to the display surface. 
   
   
     25. An image projection apparatus comprising:
 a reflective display panel for displaying a two-dimensional image on a panel display surface thereof; and 
 an oblique projection optical system for projecting the image on the panel display surface to a projection surface in such a way that a ray of light from a center of the panel display surface is obliquely incident on the projection surface, the oblique projection optical system being a substantially oblique telecentric optical system having an entrance pupil located substantially at infinity and inclined relative to an axis parallel to a height direction of the panel display surface, wherein the oblique projection optical system includes at least four curved reflecting surfaces. 
 
   
   
     26. An image projection apparatus as claimed in  claim 25 , wherein the following conditions are fulfilled:
   Fnoy≧3.5, and 
   Fnoz≧3.4, 
 where 
 Fnoy represents an f-number of the oblique projection optical system in a direction corresponding to the height direction of the panel display surface, and 
 Fnoz represents an f-number of the oblique projection optical system in a direction corresponding to the width direction of the panel display surface. 
 
   
   
     27. An image projection apparatus as claimed in  claim 25 , wherein the following conditions are fulfilled:
   Fnoy≧3.4, and 
   Fnoz≧3.3, 
 where 
 Fnoy represents an f-number of the oblique projection optical system in a direction corresponding to the height direction of the panel display surface, and 
 Fnoz represents an f-number of the oblique projection optical system in a direction corresponding to the width direction of the panel display surface. 
 
   
   
     28. An image projection apparatus as claimed in  claim 25 , wherein the image projection apparatus is a front projection apparatus. 
   
   
     29. An image projection apparatus as claimed in  claim 25 , wherein the image projection apparatus is a rear projection apparatus. 
   
   
     30. An image projection apparatus comprising:
 a reflective display panel for displaying a two-dimensional image on a panel display surface thereof; and 
 an oblique proiection optical system for projecting the image on the panel display surface to a projection surface in such a way that a ray of light from a center of the panel display surface is obliquely incident on the projection surface, the oblique projection optical system being a substantially oblique telecentric optical system having an entrance pupil located substantially at infinity and inclined relative to an axis parallel to a height direction of the panel display surface, further comprising a screen located at the projection surface, the screen including an optical member, the optical member having a Fresnel portion, 
 wherein the Fresnel portion fulfills the following condition:
   [a pitch of the Fresnel portion]/[a size of a pixel of a projected image on the screen]<0.5. 
 
 
   
   
     31. An image projection apparatus as claimed in  claim 30 , wherein the optical member is a Fresnel lens. 
   
   
     32. An image projection apparatus as claimed in  claim 31 , wherein the Fresnel lens has a flat surface on a side thereof on which projection light is incident. 
   
   
     33. An image projection apparatus as claimed in  claim 30 , wherein the optical member is a total reflection prism array. 
   
   
     34. An image projection apparatus as claimed in  claim 30 , wherein the image projection apparatus is a rear projection apparatus. 
   
   
     35. An image projection apparatus as claimed in  claim 30 , further comprising a screen located at the projection surface, wherein a portion of the oblique projection optical system protrudes from the screen. 
   
   
     36. An image projection apparatus as claimed in  claim 25 , wherein a second curved mirror as counted from a display surface side is disposed on a side of the panel display surface opposite to a first curved mirror as counted from the panel display surface. 
   
   
     37. An image projection apparatus as claimed in  claim 26 , wherein assuming that a ray of light that travels from a center of the panel display surface through a center of an aperture stop to a center of a screen surface is called a screen center ray, the following condition is fulfilled:
   0.879< DL/HL< 3.5, 
 where 
 DL represents an optical distance traveled by the screen center ray from a last surface of the projection optical system to the screen surface, and 
 HL represents a dimension of the screen surface in a direction parallel to a plane formed at the center of the projection surface by a normal to the screen surface and the screen center ray. 
 
   
   
     38. An image projection apparatus as claimed in  claim 26 , wherein assuming that a ray of light that travels from a center of the panel display surface through a center of an aperture stop to a center of a screen surface is called a screen center ray, the following condition is fulfilled:
   0.925< DL/HL< 3.5, 
 where 
 DL represents an optical distance traveled by the screen center ray from a last surface of the projection optical system to the screen surface, and 
 HL represents a dimension of the screen surface in a direction parallel to a plane formed at the center of the projection surface by a normal to the screen surface and the screen center ray.